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Intriguing Connection to Clams, Diatoms, Brown Waves and Washington / Oregon Coast

Published 11/13/22 at 5:19 PM
By Oregon Coast Beach Connection staff

Intriguing Connection to Clams, Diatoms, Brown Waves and Washington / Oregon Coast

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(Warrenton, Oregon) – Two small stretches of the Washington coast and north Oregon coast have something curious in common that also sets them apart from the rest of the region. A larger-than-usual population of diatoms makes for the oddball phenomena of brown waves and an enormous density of razor clams – as well as lots of whole sand dollars (at least in one area). (Photo of Long Beach brown waves Oregon Coast Beach Connection)

The Long Beach Peninsula, on the southern Washington coast, and Clatsop Beach, at the tip of the Oregon coast, both flank the Columbia River. It, in turn, dumps an incredible amount of nutrients into surrounding areas creating a slightly different ecosystem than the rest of the Oregon coast and Washington coastline.

For one area – right around the Necanicum River in Seaside – it's meant a lot of whole sand dollars, likely more than you can find anywhere else. If that same situation exists on the Washington side along the peninsula isn't clear, but experts say it's worth a look.

Clatsop Beach encompasses Seaside, Gearhart and Warrenton – about 20 miles. Both it and the Long Peninsula are prone to the freaky sight of thickly brown waves, which some visitors initially believe to be pollution. They can get gooey brown, with an odd kind of brown sludge at times. However, it's simply a lot of phytoplankton: a certain type known as diatoms. It's not pollution - and it's a good thing.

The populations of razor clams, the diatom brown waves and the whole sand dollars are directly related to the diatoms. It's a simple matter of the food chain, said Seaside Aquarium’s Tiffany Boothe.


Aerial shot of brown waves in Seaside (Oregon Coast Beach Connection)

“Most of the nitrates and phosphates are delivered via the Columbia River, but some also come down the Necanicum and other smaller coastal rivers,” Boothe said. “This is why there is such good razor clamming on almost all of Clatsop County beaches.”

In turn, sand dollars and razor clams feed on diatoms. With such a massive food source, this makes all of them quite prolific, down through the food chain.

The Clatsop Beach area has about 90 percent of all the razor clam population on the entire Oregon coast. The Washington coast's Long Beach area has a significant population as well.

What makes the sand dollars so prolific here is a bit of a mystery. One major factor is that they're washing up on a remote section right around the Necanicum River, at the very northern edge of Seaside and southern part of Gearhart. With fewer people, not as many are treading on them or picking them up. The diatoms are the other major factor.

But there's something about the topography of the near-shore environment that allows them to be torn out of their habitat and wash ashore.

Boothe said sand dollars live just past the surf zone in large colonies. When a sand dollar dies, its shell will end up on the beach, either via currents or strong wave action.

However, Dr. Bill Hanshumaker, when he was with the Hatfield Marine Science Center in Newport, told Oregon Coast Beach Connection several years ago there are some possibilities.

One likelihood is simply the currents in the area, as many on the north coast believe. It's clear there are more such sand dollar beds, and for some reason the currents simply dump them in one spot.

The other two possibilities have to do with terrain, Hanshumaker said. One is that there is a very flat, gently sloping beach in that spot that reaches out closer to where the beds are. The other idea has to do with erosion in one area of the sand dollar beds, where the sediment they live in is simply more prone to being churned up and disturbed.

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